bootstat: comment out duplicate entries in kBootReasonMap

Two entries can be reused. The third "unknown" entry is not really
a duplicate since the kUnknownBootReason is not checked.  Duplicate
entries reused in the future, should have
analysis/uma/configs/clearcut/TRON/histograms.xml updated first.

Test: boot_reason_test.sh
Change-Id: If2071a18160dc2c93e851fecc6b8c11fc76c9845